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Halftone Screen Calculator

What resolution a line screen actually needs.

The screen

Your image

Optional. Fill this in to check a specific file against the screen above.

Required resolution

300ppi

at final size, for a 150 lpi screen at 2×

Clears it — 423 ppi at this size

You could enlarge it to 254mm wide before it drops below the requirement.

Required resolution at final size
300 ppi
One halftone cell
0.169 mm
Actual resolution as placed
423 ppi
Placed size
180.0 × 120.0 mm
Largest usable width
254.0 mm
Scale against that maximum
71 %

Traditional screen angles

Offset from each other so the four separations do not form a moiré where they overlap. Black sits at 45° because that is the angle the eye resolves least well.

  • Cyan 15°
  • Magenta 75°
  • Yellow 0°
  • Black 45°

Enter a line screen and get the image resolution it needs, then check a specific file against it at the size you are placing it. This is where “300 ppi” comes from — and why it is the wrong answer as often as the right one.

01

Why use this tool?

The real number, not the folklore

300 ppi is 150 lpi × 2. On an 85 lpi newspaper screen you need 170, and paying for 300 wastes half the file.

Checks your actual file

Enter the pixel dimensions and the placed width and it tells you whether it clears the screen, and the largest size that would.

Quality factor explained

1.5× to 2× is the honest range, and the page says what each end costs rather than picking one for you.

Screen angles included

The four traditional angles and why black takes 45° — the other half of the question anyone asking about moiré needs.

02

How this halftone screen calculator works

A press cannot print grey. It prints solid dots at a fixed spacing — the line screen, in lines per inch — and a tone is the illusion produced by how much of each cell its dot fills. Every question about image resolution for print reduces to one thing: does the file carry enough pixels to decide what each of those dots should be?

That is what the quality factor answers. At 1× there is one pixel per halftone cell, and any pixel straddling two cells produces a visible artefact. At 2× — the Nyquist limit for a two-dimensional grid — there is enough information to resolve every dot unambiguously. Multiply the line screen by the factor and you have the resolution the file needs at final size. 150 lpi at 2× is 300 ppi, which is where the number everybody quotes actually comes from.

Between 1.5× and 2× is the working range. Below 1.5× detail visibly softens. Above 2× the extra pixels are thrown away by the screening process and buy nothing but file size and processing time — which is why supplying 600 ppi for a 150 lpi job is not twice as safe, just twice as slow.

The check against your own file is the part that catches errors. Resolution is not a property of an image; it is a property of an image at a size. A 3000 pixel photograph is 300 ppi across ten inches and 150 ppi across twenty. Placing it and then asking whether it is high enough resolution is the only order that gives a meaningful answer.

03

How to use it

  1. Step 1: Pick the line screen

    Ask the printer. 150 lpi covers most coated commercial work; uncoated stock runs coarser because the ink spreads.

  2. Step 2: Choose a quality factor

    2× unless file size is a real constraint. 1.5× is defensible and widely used.

  3. Step 3: Check your file

    Enter its pixel dimensions and the width you are placing it at. The panel tells you whether it clears the screen and how far you could enlarge it.

04

Example usage

Specifying to a photographer
Work back from the line screen and the largest size you might use, so the brief asks for the pixels the job needs rather than a round number.
Checking a stock library image
Paste the pixel dimensions and the placed width before licensing it, rather than discovering the shortfall at proof stage.
Newspaper versus magazine
The same photograph at 85 lpi and at 175 lpi needs less than half the resolution in one case. Useful when repurposing artwork across both.
05

Where the quality factor stops helping

The factor assumes the image is continuous tone — a photograph, where detail is smooth and the eye forgives interpolation. It is the wrong model for anything with hard edges. Line art, text in a screenshot, a logo or a technical drawing has no gradient for the screening to hide behind, and at 300 ppi the edges will show their steps.

Those need to be handled differently: supplied as vector where possible, or rasterised at 1,200 ppi and above as bitmap rather than greyscale. This is why a scanned signature looks wrong on an otherwise perfect page — it was treated as a photograph when it is really line art.

The other place the factor misleads is with stochastic or frequency-modulated screening, which places dots of one size at varying spacing rather than varying the dot size on a grid. There is no line screen to multiply, and the resolution requirement is set by the dot size instead. Printers using it will give you a figure; the 2× rule does not apply.

06

Frequently asked questions

Why is 300 ppi the number everybody quotes?

Because 150 lpi is the most common commercial line screen and 150 × 2 is 300. It is a correct answer to one specific question that got repeated until it sounded like a universal rule. On newsprint at 85 lpi you need 170 ppi; on a 200 lpi art book you need 400.

Is more resolution always safer?

No, just slower. Anything above the quality factor is discarded during screening, so it adds file size, processing time and RIP time without changing the printed result. The one exception is keeping headroom in case the image gets enlarged later.

What quality factor should I use?

2× if you can. It is the Nyquist limit, which means it is the point where the maths guarantees enough information rather than merely usually having enough. 1.5× is common in production and rarely visible on photographic subjects.

What is a line screen, in physical terms?

The spacing of the dot grid. At 150 lpi the cells are 1/150 inch — about 0.17mm — which is why you can see the rosette pattern in printed matter with a loupe but not with the naked eye. Coarser screens on newsprint are visible without one.

Why are the screen angles offset?

To stop the four separations forming a moiré where they overlap. Black takes 45° because that is the angle the eye resolves least well, so the most visually dominant separation is the least noticeable. Yellow takes 0° and sits only 15° from cyan, which is tolerable only because yellow is so weak.

My scan has a moiré pattern. Is that this?

Related. Scanning something already printed captures its halftone grid, which then interferes with the new screen. Descreening filters help, blurring slightly and re-sharpening helps more, and rescanning at an angle helps most — but the real answer is to find the original artwork.

07

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